Provide number of inhibitory dimensions and their gain to the ensemble.
Ensemble accepts inhibitory connections.

 - Ensemble has inhibitory connection filter
   - MCPL handler tries normal input, if this fails tries inhibitory input
   - Update code filters both normal input and inhibitory input
 - Ensemble update code computes inhibitory value and includes in neuron current
   **doesn't account for neuron gain**.
 - Inhibitory data added to SYSTEM region and regions 8 and 9 for filter and routing.